This invention relates to reflective elements and methods of making such elements, and to sensors including such elements.
Radiation pyrometers are sensors used for measuring the temperature of objects in high-temperature environments such as, turbine blades in a gas-turbine engine, or articles in a furnace. The optical components of such pyrometers must be capable of performing satisfactorily at the high-temperatures involved and, in this respect, lenses and windows can be made, for example, of sapphire of fused silica. A problem arises, however, in certain applications where it is not possible for the pyrometer or other sensor to be directly aligned with the object under observation. This can occur especially when it is desired to view the blades of a gas-turbine engine. In such circumstances it is necessary to deflect the radiation from the object into the sensor such as by use of a mirror, prism or other radiation guide. Because of the high temperatures involved in engines of this kind it has been difficult to construct such radiation guides that will perform satisfactorily. For example, conventional metal or metal-coated mirrors can oxidize rapidly with consequent loss of reflectivity. Prisms will be subject to problems caused by differential thermal expansion with respect to the component on which they are mounted, thereby rendering a secure mounting difficult to achieve.